The present invention is directed to a strap sealer. More particularly, the present invention is directed to a strap sealer having a dual action piston that is vented to increase return action.
Strap material is widely used for bundling and securing loads. These strapping materials will be commonly recognized as steel or plastic strap that surrounds or encircles a load to secure the load together, e.g., bundle the load. For example, lumber is often bundled and strapped so that the individual pieces of wood are retained within the larger lumber bundle. Many types of articles are held together by strapping material, such as paper, packaging containers, bottles and the like.
The size and strength of the strap material varies depending upon the load and the tension required in the strap. For example, in the shipping industry where large containers or crates are often secured by strapping material, large width, heavy gauge strapping is used.
When secured around a load, the strapping material must be sealed or secured to itself. Various methods and devices are known for effecting these seals. One type of strapper forms seals by punching the strapping material to form interlocks between upper and lower layers of the overlapped strapping material. This is commonly referred to as a seal-less strap. Another type of strap seal, typically for heavier gauge strapping material requires a separate seal that is positioned around the overlapped strapping material. This seal is then crimped at its edges and partially into the body of the seal and strap, transversely, of the seal to crimp the seal and the strapping material together. Deformation type seals such as these are disclosed in Meier, U.S. Pat. No. 3,089,233 and Young, U.S. Pat. No. 3,237,256, which patents are incorporated herein by reference.
To form the crimped or deformed seal, many types of sealers are known in the art. Such sealers can be driven electrically, pneumatically, hydraulically or the like. One known pneumatic sealer includes a housing having a piston that is positioned within a cylinder. The piston reciprocates to move a linkage to which a pair of jaw elements are connected. The jaw elements close or move together to contact the seal element to effect the crimp or seal. In such a pneumatic sealer, air pressure is used to move the piston to close the jaws. A spring is positioned at an opposing side of the piston to return the piston to its initial position (to open the jaws). While such an arrangement provides an effective drive for moving the jaws together, the spring continually acting on the piston tends to require an increased air pressure to move the jaws closed. In the event that the air pressure is constant, the spring slows down the action of the piston, thus slowing the overall sealing operation.
In addition, it has also been found that in this spring return arrangement, the jaws can get xe2x80x9chung-upxe2x80x9d on the seal and the spring does not have sufficient force return the piston from the closed state to the open state.
It will be recognized that in many industries in which these sealers are used, such as manufacturing or shipping industries, the time that is afforded an operator to form these seals is minimal. As such, tools having slow response times, or tools that get xe2x80x9chung-upxe2x80x9d are not acceptable in the workplace.
Accordingly, there exists a need for a sealer device that utilizes compressed air for driving a piston for moving the sealer jaws. Desirably, such a device is unbiased in that there is no constant back force on the piston as it drives the jaws closed. Most desirably, such a pneumatic sealer is fast-acting to both the sealing and opening positions, that is, to form the seal and to return to the read position.
A strap sealer having a dual action piston and a seal forming assembly operably connected to the piston. The sealer includes a housing that defines a cylinder. The housing has a penetration therein. A piston is disposed in the cylinder for reciprocating movement therein. The piston has first and second sides and defines upper and lower pressure regions at the first and second sides of the piston.
The sealer forms a seal in a seal element and the underlying steel strapping. The seal can be of the crimped or deformed type, or may be of the notch-type, in which notches are cut into the seal element and the underlying strapping material, which notched portions may also be bent to enhance seal integrity.
The piston reciprocates to move a linkage to which a pair of jaw elements are connected. The jaw elements close or move together to contact the seal element to effect the crimp or seal. The seal can be formed by crimping or by xe2x80x9cnotchingxe2x80x9d into the seal and the straps around which the seal is positioned.
The dual action piston uses compressed gas, preferably compressed air to move the piston to close the jaw elements and to move the piston to open the jaw elements. A gas inlet is in flow communication with first and second flow paths that extend between the inlet and the upper and lower pressure regions. A valve arrangement provides flow communication between the inlet and the first and second flow paths to supply and exhaust gas to the upper and lower pressure regions.
A ram is mounted to the piston for reciprocating movement therewith. The ram traverses through the housing penetration. The ram has first and second cross-sectional areas that are different from each other.
As the piston reciprocates within the housing the ram reciprocates through the housing penetration. When the ram reciprocates through the housing penetration the and the first cross-sectional area resides at the housing penetration, it forms a seal therebetween. When the second cross-sectional area passes through the housing penetration a vent path is provided from the lower pressure region outwardly to vent gas from the lower pressure region.
Advantageously, the present sealer uses a compressed gas, preferably compressed air for driving the piston for moving the sealer jaws. The present sealer uses compressed air, without a spring assist to move the piston. Thus, there is no constant back force on the piston as it drives the jaws closed. The present dual action piston is fast-acting to both the sealing and opening positions, that is, to form the seal and to return to the ready or at-rest position.
In a current embodiment, the first and second cross-sectional areas of the ram are defined by an undercut region in the ram. Preferably, the undercut region is defined by at least first and second different diameters. Most preferably, the undercut includes flats extending along a portion of the ram.
In the current embodiment, the seal forming assembly includes jaw elements that are moveable toward and away from one another between the open condition and the closed position for forming the strap seal. The vent path from the lower pressure region exhausts air from the lower pressure region when the jaw elements are moved from the open condition to the closed position. The vent path can vent to the seal forming assembly.
In a preferred embodiment, the sealer includes a sealing element at the housing penetration. The sealing element can be an O-ring or like flexible element.
These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims.